I try to make sure my rows are sewn together evenly - check by folding the quilt in half as I go is usually good enough.
On multiple borders or a medallion I do the measure top mid and bottom and cut the next border length to the average dimension.
To make sure my whole quilt top is square, I measure corner to corner in both directions. If corner to corner dimensions aren't the same, then I have to fiddle with it to adjust anything that got sewn a little crooked, or maybe just smooth it out a little better and starch, and then recheck cross wise, length wise, and kitty corner again.
Once the quilt is quilted, it is what it is and I don't mess with it. Maybe it might go out of whack because some bit is more heavily quilted? I know I started with good dimensions so I do no more than trimming off the excess, making sure my outside border width is consistent enough to give me my 1/4" seam with enough batting for a puffy binding.
I would always rather re-sew a bit here and there than cut. Cutting is not reversible! As the carpenter says when he cuts too short, put it on the board-stretcher!
